Method and apparatus for endpointing a chemical-mechanical planarization process

ABSTRACT

A method and apparatus for endpointing a planarization process of a microelectronic substrate. In one embodiment, the apparatus may include a species analyzer that receives a slurry resulting from the planarization process and analyzes the slurry to determine the presence of an endpointing material implanted beneath the surface of the microelectronic substrate. The species analyzer may include a mass spectrometer or a spectrum analyzer. In another embodiment, the apparatus may include a radiation source that directs impinging radiation toward the microelectronic substrate, exciting atoms of the substrate, which in turn produce an emitted radiation. A radiation detector is positioned proximate to the substrate to receive the emitted radiation and determine the endpoint by determining the intensity of the radiation emitted by the endpointing material. The endpointing material may be selected to be easily detected by the species detector or the radiation detector, and may further be selected to be easily distinguishable from a matrix material that comprises the bulk of the microelectronic substrate.

TECHNICAL FIELD

The present invention relates to methods and apparatuses for endpointinga chemical-mechanical planarization process.

BACKGROUND OF THE INVENTION

Mechanical and chemical-mechanical planarizing processes (collectively“CMP”) are used in the manufacturing of microelectronic devices forforming a flat surface on semiconductor wafers, field emission displaysand many other microelectronic substrates. FIG. 1 schematicallyillustrates a planarizing machine 10 with a platen or table 20, acarrier assembly 30, a polishing pad 21, and a planarizing fluid 23 onthe polishing pad 21. The planarizing machine 10 may also have anunder-pad 25 attached to an upper surface 22 of the platen 20 forsupporting the polishing pad 21. In many planarizing machines, a platendrive assembly 26 rotates (arrow A) and/or reciprocates (arrow B) theplaten 20 to move the polishing pad 21 during planarization.

The carrier assembly 30 controls and protects a substrate 80 duringplanarization. The carrier assembly 30 typically has a substrate holder32 with a pad 34 that holds the substrate 80 via suction. A carrierdrive assembly 36 typically rotates and/or translates the substrateholder 32 (arrows C and D, respectively). The substrate holder 32,however, may be a weighted, free-floating disk (not shown) that slidesover the polishing pad 21.

The combination of the polishing pad 21 and the planarizing fluid 23generally define a planarizing medium that mechanically and/orchemically-mechanically removes material from the surface of thesubstrate 80. The polishing pad 21 may be a conventional polishing padcomposed of a polymeric material (e.g., polyurethane) without abrasiveparticles, or it may be an abrasive polishing pad with abrasiveparticles fixedly bonded to a suspension material. In a typicalapplication, the planarizing fluid 23 may be a CMP slurry with abrasiveparticles and chemicals for use with a conventional nonabrasivepolishing pad. In other applications, the planarizing fluid 23 may be achemical solution without abrasive particles for use with an abrasivepolishing pad.

To planarize the substrate 80 with the planarizing machine 10, thecarrier assembly 30 presses the substrate 80 against a planarizingsurface 24 of the polishing pad 21 in the presence of the planarizingfluid 23. The platen 20 and/or the substrate holder 32 then moverelative to one another to translate the substrate 80 across theplanarizing surface 24. As a result, the abrasive particles and/or thechemicals in the planarizing medium remove material from the surface ofthe substrate 80.

CMP processes must consistently and accurately produce a uniformlyplanar surface on the substrate to enable precise fabrication ofcircuits and photo-patterns. Prior to being planarized, many substrateshave large “step heights” that create a highly topographic surfaceacross the substrate. Yet, as the density of integrated circuitsincreases, it is necessary to have a planar substrate surface at severalstages of processing the substrate because non-uniform substratesurfaces significantly increase the difficulty of forming sub-micronfeatures or photo-patterns to within a tolerance of approximately 0.1μm. Thus, CMP processes must typically transform a highly topographicalsubstrate surface into a highly uniform, planar substrate surface (e.g.,a “blanket surface”).

In the competitive semiconductor industry, it is highly desirable tomaximize the throughput of CMP processing by producing a blanket surfaceon a substrate as quickly as possible. The throughput of CMP processingis a function of several factors, one of which is the ability toaccurately stop CMP processing at a desired endpoint. In a typical CMPprocess, the desired endpoint is reached when the surface of thesubstrate is a blanket surface and/or when enough material has beenremoved from the substrate to form discrete components on the substrate(e.g., shallow trench isolation areas, contacts, damascene lines, etc.).Accurately stopping CMP processing at a desired endpoint is importantfor maintaining a high throughput because the substrate may need to bere-polished if the substrate is “under-planarized.” Accurately stoppingCMP processing at the desired endpoint is also important because toomuch material can be removed from the substrate, and thus the substratemay be “over-polished.” For example, over-polishing can cause “dishing”in shallow-trench isolation structures, or over-polishing can completelydestroy a section of the substrate. Thus, it is highly desirable to stopCMP processing at the desired endpoint.

In one conventional method for determining the endpoint of CMPprocessing, the planarizing period of one substrate in a run isestimated using the polishing rate of previous substrates in the run.The estimated planarizing period for a particular substrate, however,may not be accurate because the polishing rate may change from onesubstrate to another. Thus, this method may not accurately planarize allof the substrates in a run to the desired endpoint.

In another method for determining the endpoint of CMP processing, thesubstrate is removed from the pad and the substrate carrier, and then ameasuring device measures a change in thickness of the substrate.Removing the substrate from the pad and substrate carrier, however, istime-consuming and may damage the substrate. Thus, this method generallyreduces the throughput of CMP processing.

In still another method for determining the endpoint of CMP processing,a portion of the substrate is moved beyond the edge of the pad, and aninterferometer directs a beam of light directly onto the exposed portionof the substrate. The substrate, however, may not be in the samereference position each time it overhangs the pad. For example, becausethe edge of the pad is compressible, the substrate may not be at thesame elevation for each measurement. Thus, this method may inaccuratelymeasure the change in thickness of the wafer.

In yet another method for determining the endpoint of CMP processing,U.S. Pat. No. 5,036,015 discloses detecting the planar endpoint bysensing a change in friction between a wafer and the polishing medium.Such a change in friction may be produced by a different coefficient offriction at the wafer surface as one material (e.g., an oxide) isremoved from the wafer to expose another material (e.g., a nitride). Inaddition to the different coefficients of friction caused by a change ofmaterial at the substrate surface, the friction between the wafer andthe planarizing medium generally increases during CMP processing becausemore surface area of the substrate contacts the polishing pad as thesubstrate becomes more planar. U.S. Pat. No. 5,036,015 disclosesdetecting the change in friction by measuring the change in currentthrough the platen drive motor and/or the drive motor for the substrateholder. One drawback with this method, however, is that it does notallow for endpointing within a generally homogeneous substrate thatconsists of a single material.

In still a further method for determining the endpoint of CMPprocessing, such as is disclosed in U.S. Pat. No. 5,559,428, thechemical composition of the CMP slurry is analyzed to determine when alayer of a first material has been removed to expose a layer of asecond, different, material. For example, planarization may continuethrough the first material until the second material is exposed, atwhich point some of the second material is removed and enters theslurry. The second material in the slurry is identified usinginstrumentation such as inductively coupled plasma for atomic emissionspectroscopy, and the planarization process is halted. Like theabove-described technique for sensing a change in planarizing function,this technique also does not allow endpointing within a generallyhomogeneous substrate.

SUMMARY OF THE INVENTION

The present invention is directed toward methods and apparatuses forendpointing a planarizing process of a microelectronic substrate. In oneembodiment, the microelectronic substrate includes a matrix material andan endpointing material implanted or otherwise positioned beneath asurface of the matrix material at the desired endpoint location. Theapparatus may include a first portion and a second portion movablerelative to each other to remove material from the microelectronicsubstrate positioned therebetween. The removed material may betransported to a species detector to detect the presence of theendpointing material. For example, the endpointing material may bedetected by determining an atomic mass of the endpointing material, orby determining an intensity of radiation emitted by atoms of theendpointing material.

In another embodiment, the apparatus may be include a radiation sourcethat directs impinging radiation toward the microelectronic substratewhile the substrate is planarized. The apparatus may further include adetector spaced apart from the microelectronic substrate to receiveradiation emitted by atoms of the substrate while the atoms remainattached to the microelectronic substrate. The endpointing material maybe selected to emit radiation at a wavelength different than radiationemitted by the matrix material so that when the second material isexposed during planarization, it may be easily identified by thedetector and planarization may be halted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional elevation view of achemical-mechanical planarization machine in accordance with the priorart.

FIG. 2 is a partially schematic, partial cross-sectional elevation viewof a chemical-mechanical planarization machine in accordance with anembodiment of the invention.

FIG. 3A is a cross-sectional elevation view of a portion of amicroelectronic substrate having an endpointing material in accordancewith another embodiment of the invention.

FIG. 3B is a graph of the concentration of the endpointing material inthe substrate shown in FIG. 3A as a function of depth beneath a surfaceof the substrate.

FIG. 4A is a cross-sectional elevation view of a portion of amicroelectronic substrate having an endpointing material in accordancewith another embodiment of the invention.

FIG. 4B is a graph of the concentration of the endpointing material inthe substrate shown in FIG. 4A as a function of depth beneath a surfaceof the substrate.

FIG. 5A is a cross-sectional elevation view of a portion of amicroelectronic substrate having adjacent layers of an endpointingmaterial in accordance with yet another embodiment of the invention.

FIG. 5B is a graph of the concentration of the endpointing material inthe substrate shown in FIG. 5A as a function of depth beneath a surfaceof the substrate.

FIG. 6 is a cross-sectional elevation view of a portion of amicroelectronic substrate in accordance with still another embodiment ofthe invention.

FIG. 7 is a partially schematic, partial cross-sectional elevation viewof a chemical-mechanical planarization machine in accordance withanother embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed toward methods and apparatuses forendpointing the planarization of a microelectronic substrate. Themicroelectronic substrate may include an endpointing material positionedbeneath a surface of the substrate, and the apparatus may include adetector that detects the presence of the endpointing material before orafter the overlaying substrate material has been removed. Many specificdetails of certain embodiments of the invention are set forth in thefollowing description and in FIGS. 2-7 to provide a thoroughunderstanding of such embodiments. One skilled in the art, however, willunderstand that the present invention may have additional embodimentsand that they may be practiced without several of the details describedin the following description.

FIG. 2 illustrates a CMP apparatus 110 having a platen 120 and aplanarizing medium 127. In the embodiment shown in FIG. 2, theplanarizing medium 127 includes a polishing pad 121 releasably attachedto the platen 120, and a planarizing fluid 123 disposed on a planarizingsurface 124 of the polishing pad 121. The platen 120 may be movable bymeans of a platen drive assembly 126 that may impart rotational motion(indicated by arrow A) and/or translational motion (indicated by arrowB) to the platen 120. As was discussed above, the CMP apparatus 110 mayalso include a carrier assembly 130 having a substrate holder 132 and aresilient pad 134 that together press a microelectronic substrate 180against the planarizing surface 124 of the polishing pad 121. A carrierdrive assembly 136 may be coupled to the carrier assembly 130 to movethe carrier assembly axially (indicated by arrow C) and/or rotationally(indicated by arrow D) relative to the platen 120.

The apparatus 110 may further include a liquid supply tube 129 thatsupplies the planarizing fluid 123 to the planarizing surface 124 of thepolishing pad 121. The planarizing fluid 123 may be an inert,non-abrasive liquid, such as water, or the planarizing fluid may bechemically active and may further include abrasive particles tochemically and/or mechanically planarize the microelectronic substrate180. As the carrier assembly 130 moves relative to the platen 120, theplanarizing medium 127 (i.e., the platen 121 and/or the planarizingfluid 123) removes material from the microelectronic substrate 180. Theremoved material may include a matrix material 181 that forms the bulkof the microelectronic substrate 180 and may also include an endpointingmaterial 182 disposed beneath the surface of the matrix material 181.For purposes of clarity, the deposits of the endpointing material 182are shown enlarged in FIG. 2 relative to the surrounding matrix material181. The material removed from the substrate 180 may mix with theplanarizing fluid 123 to form a slurry 128 that is moved by a transportdevice 160 from the platen 120 to a species analyzer 140 where theslurry 128 is analyzed to determine the presence or absence of theendpointing material 182.

In one embodiment, the transport device 160 may include a closed conduit161 coupled at one end to the platen 120, and in other embodiments, thetransport device 160 may include other fluid conveyance means, such asan open channel. The conduit 161 may include a drain valve 162 to drainthe slurry 128 prior to storing or maintaining components of theapparatus 110. The conduit 161 may be coupled to a pump 163 that pumpsthe slurry 128 toward the species analyzer 140, and the conduit may alsobe coupled to one or more conditioning devices that condition the slurry128 before it reaches the species analyzer 140. For example, theconditioning devices may include a diluter 164 that dilutes the slurry128 if the expected concentration of the endpointing material 182 mayexceed the capacity of the species analyzer 140. The conditioningdevices may further include a filter 165 to separate abrasive particlesfrom the slurry 128, and/or an optional vaporizer 166 to vaporize theslurry 128 and provide gas-phase atoms to the species analyzer 140.

The species analyzer 140 may include any number of devices that candetermine the presence of the endpointing material in the slurry 128 orcan determine a concentration of the endpointing material 182 relativeto a concentration of the matrix material 181. For example, in oneembodiment, the species analyzer 140 may include a mass spectrometer,such as is available from SRC Corporation of Sunnyvale, California. Themass spectrometer may impart a charge to atoms of both the matrixmaterial 181 and the endpointing material 182 and may pass the atomsthrough a magnetic field. The atoms of the endpointing material 182 maybe selected to have a different atomic mass than the atoms of the matrixmaterial 181, such that the atoms of the endpointing material 182 may bedeflected by the magnetic field along a path that is different that thepath followed by atoms of the matrix material 181. Accordingly, theconcentration of the atoms of each type of material may be determined bymeasuring the number of atoms deflected along each corresponding path.For example, the number of deflected atoms may be determinedelectrically by measuring a current generated by the atoms as theystrike a metal plate, or the number of atoms may be determined visuallyby observing photographic plates on which the atoms impinge. In otherembodiments, other means may be used to measure the presence and/orconcentration of the deflected atoms.

In an alternate embodiment, the species analyzer 140 may include aspectrum analyzer that determines the intensity of light emitted by theexcited atoms at a characteristic wavelength. Accordingly, theendpointing material 182 may be selected to emit light at thecharacteristic wavelength, and the matrix material 181 may be selectedto emit light at a wavelength other than the characteristic wavelength.The presence and/or concentration of the endpointing material 182 in theslurry may then be determined by detecting an increase in the intensityof light emitted at the characteristic wavelength. The spectrum analyzermay include conventional means, such as a laser radiation source, toexcite the atoms. Similarly, conventional detectors may be used todetermine the intensity of the light emitted by the excited atoms.

The species analyzer 140 may be coupled to a controller 150 which is inturn coupled to the platen drive assembly 126 and the carrier driveassembly 136. Accordingly, when the species analyzer 140 detects theendpointing material 182 in the slurry 128, it may send a control signalto the controller 150 which halts planarization of the microelectronicsubstrate 180 by stopping relative motion between the carrier assembly130 and the platen 120. Because it may be desirable to halt theplanarizing process as soon as the endpointing material 182 is exposed,the components of the planarizing apparatus 110 may be selected toreduce the time that elapses between exposing the endpointing material182 and halting the planarizing process. For example, the conduit 161may be made as short as possible to reduce fluid residence time withinthe conduit, and the pump 163 may be sized to pass the slurry 128quickly through the conduit 161. The species analyzer 140 may beselected to quickly analyze the slurry 128, and the controller 150 maybe selected to deliver control signals to the drive assemblies 126 and136 in a short period of time. Accordingly, in one embodiment, theapparatus 110 may halt the planarization process within five seconds ofexposing the endpointing material 182. In other embodiments, theapparatus 110 may halt the planarizing process in shorter or longerperiods of time, depending on variables such as the planarizing rate andthe composition of the microelectronic substrate 180.

FIG. 3A is a detailed cross-sectional elevation view of a portion of themicroelectronic substrate 180 shown in FIG. 2. As shown in FIG. 3A, theendpointing material 182 is disposed beneath an upper surface 183 of thematrix material 181. The upper surface 183 may include a plurality ofrecesses 184 and raised features 187 that are removed to the level ofthe recesses 184 during planarization.

In one embodiment, the matrix material 181 may include a semiconductormaterial, such as silicon, tetraethylorthosilicate or borophosphatesilicon glass, and in other embodiments, the matrix material 181 mayinclude other substances. The endpointing material 182 may includetungsten, aluminum, copper, or any material that can be distinguishedfrom the matrix material 181 with the species analyzer 140 (FIG. 2). Forexample, the matrix material 181 may include any silicon compound andthe endpointing material 182 may include any non-silicon compound orelement. In one embodiment, the endpointing material 182 may have such anegligible effect on the electrical properties of the microelectronicsubstrate 180 that the performance of the microelectronic substrate ifnone or only a portion of the endpointing material 182 is removed duringplanarization is unchanged from that of microelectronic substrate thatconsists of only the matrix material 181. In other embodiments, theendpointing material 182 may have an affect on the electrical propertiesof the microelectronic substrate 180 and may accordingly be left in themicroelectronic substrate 180 after planarization (if the effect isbeneficial) or completely removed from the microelectronic substrate 180during planarization (if the effect is adverse).

In one embodiment, the endpointing material 182 may be implanted in thematrix material 181 by ionizing atoms of the endpointing material tocreate charged atoms and accelerating the charged atoms through anelectric field toward the microelectronic substrate 180, as indicated byarrow E. The charged atoms have sufficient force to penetrate into thematrix material 181 to a selected depth D. The ionized atoms mayaccordingly form upper and lower layers 185 (shown as 185 a and 185 b,respectively), each having a thickness t. The upper layers 185 a arepositioned beneath the raised features 187 and the lower layers 185 bare positioned beneath the recesses 184.

The depth D to which the endpointing material atoms penetrate may becontrolled by selecting the endpointing material 182 and the matrixmaterial 181, and by controlling the charge on the ionized endpointingmaterial atoms and the acceleration imparted to the charged atoms. Thethickness t and the concentration of the endpointing material atomswithin the layers 185 may be controlled by varying the depth D as theions are implanted and/or by controlling the time during which themicroelectronic substrate 180 is exposed to the ions. For example, inone embodiment, the layers 185 a and 185 b may have a thickness in therange of approximately 100 Å to approximately 500 Å and may bepositioned approximately 200 Å beneath the raised features 187 and therecesses 184, respectively. In other embodiments, the depth D andthickness t of the layers 185 may have other values depending on theselected endpointing material 182 and the matrix material 181, andwhether or not the endpointing material 182 is to remain in themicroelectronic substrate 180 after planarization. In one embodiment,the atomic concentration of the endpointing material may be in the rangeof approximately 0.1% to approximately 0.001% (i.e., the number ofendpointing material atoms within the layers 185 may be in the range ofapproximately 0.1% to approximately 0.001% of the number of matrixmaterial atoms in the layers 185). In other embodiments, theconcentration of endpointing material atoms may have other values,depending on the sensitivity of the species analyzer 140 (FIG. 2.)

FIG. 3B is a graph of the concentration of the endpointing material 182as a function of depth beneath the surface 183 of the microelectronicsubstrate 180 shown in FIG. 3A. As shown in FIG. 3B, the concentrationprofile has two spikes 186 (shown as 186 a and 186 b) corresponding tothe upper and lower layers 185 a and 185 b, respectively (FIG. 3A).Accordingly, in one method of operation, the microelectronic substrate180 shown in FIG. 3A is placed with the upper surface 183 facingdownward against the polishing pad 121 shown in FIG. 2. Themicroelectronic substrate 180 is moved relative to the polishing pad 121to remove material from the substrate, and the material is conveyed bythe transport device 160 (FIG. 2) to the species analyzer 140 (FIG. 2).As the microelectronic substrate 180 is planarized, the species analyzer140 may produce a concentration profile similar to that shown in FIG.3B, based on the atomic mass or characteristic wavelength of atoms inthe slurry 128, as discussed above with reference to FIG. 2. Theapparatus 110 (FIG. 2) continues to planarize the substrate 180 afterthe species analyzer 140 detects upper layer 185 a (corresponding to theupper spike 186 a), until the species analyzer 140 detects the lowerlayer 185 b (corresponding to the lower spike 186 b). Where theendpointing material 182 has a negligible or beneficial effect on theelectrical properties of the microelectronic substrate 180, theplanarizing process may be halted before the lower layer 185 b of theendpointing material 182 is completely removed. Alternatively, where theendpointing material 182 has an adverse effect on the electricalproperties of the microelectronic substrate 180, planarization maycontinue until the endpointing material 182 has been completely removed.

One advantage of an embodiment of the method and apparatus describedabove with respect to FIGS. 2-3B is that the planarizing process may beaccurately halted after material has been removed from a generallyhomogeneous microelectronic substrate 180. Unlike some conventionalmethods, which may require a relatively large, continuous layer ofmaterial different in composition than that of the substrate to detectthe endpoint, the present method may be used to endpoint amicroelectronic substrate 180 that is homogeneous except for theaddition of a small amount of the endpointing material 182.

Another advantage is that the endpoint may be determined in situ,without removing the substrate 180 from the planarizing apparatus 110.This is so because the transport means 160 and the species analyzer 140may operate without interrupting or otherwise affecting the planarizingprocess. Still another advantage is that the position of the endpointmay be selected by controlling the depth at which the endpointingmaterial 182 is deposited in the microelectronic substrate 180.Furthermore, the microelectronic substrate 180 may be manufactured withseveral layers 185, each positioned at a different depth beneath thesurface 183. The different depths may result from the topography of thesurface 183, or alternatively, the implanting process may be controlledto position each layer 185 at a selected depth beneath the surface 183.During planarization, one of the layers 185 may then be selected tocorrespond to the desired endpoint.

FIG. 4A is a cross-sectional elevation view of a portion of amicroelectronic substrate 280 having two types of recesses 284, shown inFIG. 4A as shallow recesses 284 a and deep recesses 284 b, eachpositioned at a different depth beneath the upper surface 283.Accordingly, the endpointing material 282 may form three layers 285(shown as 285 a, 285 b, and 285 c) when the endpointing material isimplanted from above the upper surface 283. Upper layers 285 a may bepositioned directly beneath raised features 287, intermediate layers 285b may be positioned beneath the shallow recesses 284 a, and lower layers285 c may be positioned beneath the deep recesses 284 b. Theconcentration profile of the endpointing material 282 is shown in FIG.4B as a function of depth beneath the upper surface 283. As shown inFIG. 4B, the profile includes three spikes 286 (shown as 286 a, 286 b,and 286 c), corresponding to the respective layers 285.

In operation, the microelectronic substrate 280 may be planarized untilthe lowermost layer 285 c (corresponding to the lowermost spike 286 c)has been detected. As discussed above with respect to FIGS. 2-3B, thelowermost layer 285 c may be removed or retained, depending upon thecharacteristics of the endpointing material 282. Where the number oftypes of recesses 284 in the upper surface of the microelectronicsubstrate is known in advance, the planarizing apparatus 110 (FIG. 2)may be configured or programmed to halt the planarizing processautomatically upon detecting the lowermost layer 285 c of endpointingmaterial 282. For example, the planarizing apparatus 110 may beprogrammed to stop planarization after detecting two concentrationspikes 186 (e.g., for the microelectronic substrate 180 shown in FIG.3A), or may be halted after detecting three concentration spikes 286(for the microelectronic substrate 280 shown in FIG. 4A). In otherembodiments, the planarizing apparatus 110 may be programmed to haltplanarization based on a different number of concentration spikes,depending upon the topography of the particular type of microelectronicsubstrate. This method of operation may be particularly advantageouswhere, as may often be the case, the number of types of recesses isknown for a particular substrate manufacturing process or a particularbatch of microelectronic substrates.

FIG. 5A is a cross-sectional elevation view of a portion of amicroelectronic substrate 380 having adjacent layers 385 a and 385 bpositioned beneath raised features 387 and recesses 384, respectively.As shown in FIG. 5A, each of the layers 385 has a thickness t₁ that isgreater than a distance d between the upper surface 383 and the bottomsof the recesses 384. Accordingly, the layers 385 a and 385 b overlap inthe sense that they are both present over a certain range of depthsbeneath the upper surface 383 of the microelectronic substrate 380. As aresult, the concentration profile of the endpointing material 382 in themicroelectronic substrate 380 has a single continuous spike 386, asshown in FIG. 5B.

An advantage of the overlapping layers 385 a and 385 b shown in FIG. 5Ais that an effectively continuous layer of endpointing material 382 maybe implanted beneath the upper surface 383 of the microelectronicsubstrate 380 by making the thickness t₁ of the layers 385 greater thanthe depth d of the recesses 384. Accordingly, a user need not track thenumber of layers 385 that must be detected before reaching the endpoint.Conversely, an advantage of the substrates 180 and 280 shown in FIGS. 3Aand 4A is that the user need only know the number of types of recessesfor each substrate and need not know the depth of the recesses beneaththe substrate upper surface.

FIG. 6 is a cross-sectional elevation view of a portion of amicroelectronic substrate 480 having a smooth, continuous layer 485 ofan endpointing material 482. Where the upper surface 483 of themicroelectronic substrate 480 is generally flat, the layer 485 may beformed by ion implantation, as was discussed above generally withreference to FIG. 2. Alternatively, the microelectronic substrate 480may be formed by depositing the layer 485 between a lower layer 481 aand an upper layer 48 b of the matrix material 481. The layer 485 mayaccordingly be formed using chemical vapor deposition, sputtering, orother conventional methods.

An advantage of the microelectronic substrate 480 shown in FIG. 6 isthat it may be planarized without knowledge of the number or size of anysurface features. Conversely, an advantage of the substrates shown inFIGS. 3A, 4A and 5A is that it may be easier to implant the endpointingmaterial in the matrix material than it is to separately form the upperand lower layers 481 a, 481 b of the matrix material 481 shown in FIG.6.

FIG. 7 is a partially schematic, partial cross-sectional elevation viewof a CMP machine 510 having a species detector 540 that generates anddetects radiation in accordance with another embodiment of theinvention. The species analyzer 540 may include a radiation source 543(for example, a laser) that generates incident radiation 544 (forexample, laser radiation) and directs the incident radiation toward themicroelectronic substrate 180. Accordingly, the platen 120, polishingpad 121, and an under pad 525 may have a series of aligned apertures 549that extend continuously from the radiation source 543 to the uppersurface 183 of the microelectronic substrate 180. The apertures 549 maybe filled with a solid window 548 formed from a quartz crystal or othertransparent or nearly transparent material.

The species analyzer 540 may further include a radiation detector 546positioned beneath the window 548 to receive radiation 545 emitted bythe microelectronic substrate 180. The radiation detector 546 andradiation source 543 may be controlled by a controller 550 that alsocontrols operation of the platen drive assembly 126 and the carrierdrive assembly 136. The radiation detector 546 may be tuned to receivejust the radiation emitted by the endpointing material 182. Accordingly,the endpointing material 182 may be selected to emit radiation at awavelength different that radiation emitted by the matrix material 181.Alternatively, the radiation detector 546 may detect a range ofradiations but may display or send to the controller 550 signalscorresponding only to the selected emitted radiation. Furthermore, theradiation source 543 may be selected to preferentially excite atoms ofthe endpointing material 182, rather than the matrix material 181.Alternatively, the radiation source 543 may be selected topreferentially excite atoms of the matrix material 181.

In operation, the radiation source 543 is activated to direct theincident radiation 544 toward the upper surface 183 of the substrate180. The incident radiation 544 may penetrate the upper surface 183 toexcite atoms within the microelectronic substrate 180 to a higher energylevel. As the atoms descend from the higher energy level, they producethe emitted radiation 545 that passes back through the window 548 to theradiation detector 546.

As planarization progresses, matrix material 181 between the endpointingmaterial 182 and the upper surface 183 is removed, increasing the amountof incident radiation 544 impinging on the endpointing material 182, andaccordingly increasing the emitted radiation 545 emitted by theendpointing material and detected by the radiation detector 546. Infact, depending on the intensity of the incident radiation 544 and/orthe characteristics of the matrix material 181, the incident radiationmay penetrate enough of the matrix material 181 to excite theendpointing material atoms even before planarization begins. As materialis removed from the microelectronic substrate 180, the portion of theemitted radiation 545 corresponding to the endpointing material 182 anddetected by the detector 546 continues to increase until the endpointingmaterial 182 is completely exposed, and then decreases as theendpointing material 182 is removed. The controller 550 may halt theplanarizing process when the endpointing material 182 is detected, orafter the endpointing material 182 has been removed, as was discussedabove with reference to FIG. 2.

One advantage of the CMP machine 510 shown in FIG. 7 is that it does notrequire removing a slurry from the platen 120. Accordingly, themechanical complexity of the CMP machine 510 may be reduced.Furthermore, the time between the exposure and the detection of theendpointing material 182 may be reduced because the endpointing materialis not transported away from the platen 120 for analysis. Anotheradvantage is that the presence of the endpointing material 182 may bedetected before planarization begins because the incident radiation 544may penetrate the upper surface 183 of the microelectronic substrate180. Accordingly, a user can continuously monitor the proximity of theendpointing material 182 to the upper surface 183.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

What is claimed is:
 1. In a planarizing process of a microelectronicsubstrate that includes first and second substances, the secondsubstance being beneath a surface of the microelectronic substrate, amethod of endpointing the planarizing process, comprising: removingmaterial from the microelectronic substrate to expose the secondsubstance; detecting the second substance while removing material fromthe microelectronic substrate by detecting an intensity of light at aselected wavelength emitted by atoms of the second substance while thesecond substance remains implanted in the microelectronic substrate; andremoving a sufficient amount of the second substance from themicroelectronic substrate such that electrical characteristics of themicroelectronic substrate are generally the same as those of themicroelectronic substrate without the second substance.
 2. The method ofclaim 1, further comprising implanting the second substance beneath thesurface of the microelectronic substrate.
 3. The method of claim 2wherein atoms of the second substance have an electrical charge andimplanting the second substance includes positioning the atoms of thesecond substance proximate to a like electrical charge to accelerate theatoms of the second substance toward the microelectronic substrate. 4.The method of claim 1, further comprising: applying the second substanceto a surface of the first substance; and applying an additional amountof the first substance to the second substance.
 5. The method of claim 4wherein the act of applying the second substance includes depositing thesecond substance on the surface of the first substance while the secondsubstance is a vapor.
 6. A method of planarizing a surface of amicroelectronic substrate, comprising: placing an endpointing substancein the substrate beneath the surface of the substrate solely for thepurpose of endpointing the planarizing of the substrate; abrasivelyremoving material from the substrate at least to the level of theendpointing substance; detecting when the endpointing substance is beingabrasively removed along with the abrasive removal of the material fromthe substrate by detecting an intensity of light at a selectedwavelength emitted by atoms of the second substance while the secondsubstance remains implanted in the microelectronic substrate; andterminating the abrasive removal of the material from the substrateresponsive to detecting the abrasive removal of the endpointingsubstance.
 7. The method of claim 6 wherein the abrasive removal ofmaterial from the substrate occurs in the presence of a planarizingfluid, and wherein the act of detecting the endpointing substancecomprises analyzing the planarizing fluid to detect the presence of theendpointing substance in the planarizing fluid.
 8. The method of claim 6wherein the abrasive removal of material from the substrate includesremoving some of the endpointing substance.
 9. The method of claim 6wherein the abrasive removal of material from the substrate includesremoving approximately all of the endpointing substance.
 10. In aplanarizing process of a microelectronic substrate that includes a firstsubstance, a method of endpointing the planarizing process, comprising:incorporating an amount of a second substance into the microelectronicsubstrate by implanting the second substance in the first substance andbeneath a surface of the microelectronic substrate; reducing a thicknessof the microelectronic substrate by removing material from themicroelectronic substrate to expose the second substance; detecting thesecond substance by analyzing material of the microelectronic substrateby detecting an intensity of light at a selected wavelength emitted byatoms of the second substance while the second substance remainsimplanted in the microelectronic substrate; and further reducing thethickness of the microelectronic substrate by removing approximately theentire amount of the second substance from the microelectronicsubstrate.
 11. The method of claim 10 wherein atoms of the secondsubstance have an electrical charge and implanting the second substanceincludes positioning the atoms of the second substance proximate to alike electrical charge to accelerate the atoms of the second substancetoward the microelectronic substrate.
 12. The method of claim 10 whereinimplanting the second substance includes forming a layer of the secondsubstance within the microelectronic substrate.
 13. The method of claim12 wherein forming a layer includes forming a layer having a thicknessin the range of approximately 100 Angstroms to approximately 500Angstroms.
 14. The method of claim 12 wherein forming a layer includesforming a layer centered at approximately 200 Angstroms beneath thesurface of the microelectronic substrate.
 15. The method of claim 12wherein forming a layer includes forming a layer having a number ofatoms of the second substance in the range of approximately 0.1% toapproximately 0.001% of the number of atoms of the first substance. 16.The method of claim 10 wherein detecting the second substance includesdetecting a layer of the second substance.
 17. The method of claim 10wherein the surface of the microelectronic substrate is a first surface,the microelectronic substrate having a second surface opposite the firstsurface, further wherein the first surface includes a first portionhaving a first height relative to the second surface and a secondportion having a second height relative to the second surface differentthan the first height, further wherein the act of implanting the secondsubstance includes implanting a first amount of the second substance ata first selected depth beneath the surface of the microelectronicsubstrate at the first portion and implanting a second amount of thesecond substance at a second selected depth beneath the surface of themicroelectronic device at the second portion, the first and seconddepths being approximately equal.
 18. The method of claim 17, furthercomprising ceasing to remove material from the microelectronic substrateafter detecting the first and second portions of the second substance.19. The method of claim 10, further comprising ceasing to removematerial from the microelectronic substrate after detecting the secondsubstance.
 20. In a planarizing process of a microelectronic substratethat includes a first substance, a method of endpointing the planarizingprocess, comprising: incorporating a second substance into themicroelectronic substrate; removing material from the microelectronicsubstrate to expose the second substance; removing at least a portion ofthe second substance from the microelectronic substrate; and detectingthe portion of the second substance by detecting an intensity of lightat a selected wavelength emitted by atoms of the second substance whilethe second substance remains implanted in the microelectronic substrate.21. The method of claim 20 wherein incorporating the second substanceincludes implanting the second substance beneath a surface of the firstsubstance.
 22. The method of claim 21 wherein atoms of the secondsubstance have an electrical charge and the act of implanting the secondsubstance includes positioning the atoms of the second substanceproximate to a like electrical charge to accelerate the atoms of thesecond substance toward the microelectronic substrate.
 23. The method ofclaim 22 wherein incorporating the second substance includes: applyingthe second substance to a surface of the first substance; and applyingan additional amount of the first substance to the second substance. 24.The method of claim 23 wherein the act of applying the second substanceincludes depositing the second substance on the surface of the firstsubstance while the second substance is in vapor form.
 25. The method ofclaim 20 wherein removing material from the microelectronic substrateincludes engaging a planarizing liquid with the microelectronicsubstrate and removing the second substance from the microelectronicsubstrate includes mixing a portion of the second substance with theplanarizing liquid, further comprising vaporizing at least some of theplanarizing liquid and the portion of the second substance in theplanarizing liquid.
 26. The method of claim 20 wherein the surface ofthe microelectronic substrate is a first surface, the microelectronicsubstrate having a second surface opposite the first surface, furtherwherein the first surface includes a first portion having a first heightrelative to the second surface and a second portion having a secondheight relative to the second surface different than the first height,further wherein the act of implanting the second substance includesimplanting a first amount of the second substance at a first selecteddepth beneath the surface of the microelectronic substrate at the firstportion and implanting a second amount of the second substance at asecond selected depth beneath the surface of the microelectronic deviceat the second portion, the first and second depths being approximatelyequal.
 27. The method of claim 26, further comprising ceasing to removematerial from the microelectronic substrate after detecting the firstand second portions of the second substance.
 28. The method of claim 20,further comprising ceasing to remove material from the microelectronicsubstrate after detecting the second substance.
 29. In a planarizingprocess of a microelectronic substrate that includes a first substance,a method of endpointing the planarizing process, comprising: implantinga second substance beneath a surface of the microelectronic substrate;removing material from the microelectronic substrate to expose thesecond substance; removing at least a portion of the second substance;and detecting light emitted by atoms of the second substance at aselected wavelength while the second substance remains implanted in themicroelectronic substrate.
 30. The method of claim 29 wherein the act ofdetecting light emitted by atoms of the second substance includesdetecting an intensity of the light at a selected wavelength.
 31. Themethod of claim 29, further comprising comparing an intensity of lightemitted by atoms of the second substance to an intensity of lightemitted by atoms of the first substance.
 32. The method of claim 29,further comprising exciting atoms of the second substance.
 33. Themethod of claim 29 wherein removing material from the microelectronicsubstrate includes exposing the microelectronic substrate to aplanarizing liquid and removing the second substance from themicroelectronic substrate includes mixing a portion of the secondsubstance with the planarizing liquid, further comprising vaporizing atleast some of the planarizing liquid and the portion of the secondsubstance in the planarizing liquid.
 34. The method of claim 29 whereinatoms of the second substance have an electrical charge and implantingthe second substance includes positioning the atoms of the secondsubstance proximate to a like electrical charge to accelerate the atomsof the second substance toward the microelectronic substrate.
 35. Themethod of claim 29 wherein the surface of the microelectronic substrateis a first surface, the microelectronic substrate having a secondsurface opposite the first surface, further wherein the first surfaceincludes a first portion having a first height relative to the secondsurface and a second portion having a second height relative to thesecond surface different than the first height, further wherein the actof implanting the second substance includes implanting a first amount ofthe second substance at a first selected depth beneath the surface ofthe microelectronic substrate at the first portion and implanting asecond amount of the second substance at a second selected depth beneaththe surface of the microelectronic device at the second portion, thefirst and second depths being approximately equal.
 36. The method ofclaim 35, further comprising removing the first and second portions ofthe first surface.
 37. The method of claim 35, further comprisingceasing to remove material from the microelectronic substrate afterdetecting the first and second portions of the second substance.
 38. Themethod of claim 29, further comprising ceasing to remove material fromthe microelectronic substrate after detecting the second substance. 39.In a planarizing process of a microelectronic substrate that includes afirst substance, a method of endpointing the planarizing process,comprising: implanting a second substance beneath a surface of themicroelectronic substrate; directing laser radiation toward the surfaceof the microelectronic substrate and exciting atoms impinged by thelaser radiation removing material from the microelectronic substrate toexpose the second substance; detecting the second substance bydetermining an intensity of light emitted by excited atoms of the secondsubstance while the second substance is attached to the microelectronicsubstrate; and removing a sufficient amount of the second substance fromthe microelectronic substrate such that electrical characteristics ofthe microelectronic substrate are generally the same as those of themicroelectronic substrate without the second substance.
 40. The methodof claim 39, further comprising selecting a wavelength of the laserradiation to excite atoms of the first substance to a first selectedlevel and excite atoms of the second substance to a second selectedlevel, the second selected level being higher than the first selectedlevel.
 41. The method of claim 39 wherein the act of removing materialfrom the microelectronic substrate includes exposing the microelectronicsubstrate to a planarizing liquid and the step of removing the secondsubstance from the microelectronic substrate includes mixing a portionof the second substance with the planarizing liquid, further comprisingvaporizing at least some of the planarizing liquid and the portion ofthe second substance in the planarizing liquid.
 42. The method of claim39 wherein atoms of the second substance have an electrical charge andimplanting the second substance includes positioning the atoms of thesecond substance proximate to a like electrical charge to accelerate theatoms of the second substance toward the microelectronic substrate. 43.The method of claim 39 wherein the surface of the microelectronicsubstrate is a first surface, the microelectronic substrate having asecond surface opposite the first surface, further wherein the firstsurface includes a first portion having a first height relative to thesecond surface and a second portion having a second height relative tothe second surface different than the first height, further wherein theact of implanting the second substance includes implanting a firstamount of the second substance at a first selected depth beneath thesurface of the microelectronic substrate and implanting a second amountof the second substance at the first portion and at a second selecteddepth beneath the surface of the microelectronic device at the secondportion, the first and second depths being approximately equal.
 44. Themethod of claim 43, further comprising removing material from the firstand second portions of the first surface.
 45. The method of claim 43,further comprising ceasing to remove material from the microelectronicsubstrate after detecting the first and second portions of the secondsubstance.
 46. The method of claim 39, further comprising ceasing toremove material from the microelectronic substrate after detecting thesecond substance.
 47. A microelectronic substrate, comprising: asemiconductor material; and an endpointing material positioned beneath asurface of the semiconductor material, the amount of endpointingmaterial in the semiconductor material being such that electricalcharacteristics of the semiconductor material with the endpointingmaterial positioned beneath the surface of the semiconductor materialare generally the same as electrical properties of the semiconductormaterial without the endpointing material.
 48. The substrate of claim 47wherein the endpointing material includes a layer of endpointingmaterial atoms located a selected distance beneath the surface of thesemiconductor material.
 49. The substrate of claim 47 wherein thesemiconductor material includes silicon and the endpointing material isselected from tungsten, copper and aluminum.
 50. The substrate of claim47 wherein the semiconductor material is selected fromtetraethylorthosilicate and borophosphate silicon glass and theendpointing material does not include silicon.
 51. The substrate ofclaim 47 wherein the semiconductor material includes a first substancehaving a first atomic mass and the endpointing material includes asecond substance having a second atomic mass different than the firstatomic mass.
 52. The substrate of claim 47 wherein the semiconductormaterial includes first atoms that emit light at a first characteristicwavelength and the endpointing material includes second atoms that emitlight at a second characteristic wavelength that is different than thefirst characteristic wavelength.
 53. The substrate of claim 47 whereinthe semiconductor material includes first atoms that emit light having afirst intensity when impinged by laser radiation at a selectedradiation, and the endpointing material includes second atoms that emitlight having a second intensity when impinged by the selected laserradiation, the first intensity being different than the secondintensity.
 54. The substrate of claim 47 wherein the endpointingmaterial includes ionized atoms.
 55. An apparatus for detecting theendpoint of a planarizing process of a microelectronic substrate havinga first substance and a second substance, the second substance beingbeneath a surface of the microelectronic substrate, the apparatuscomprising: a planarizing device having a first portion and a secondportion movable relative to the first portion to remove material fromthe microelectronic substrate positioned therebetween, the materialincluding atoms of the first and second substances; transport means tomove the material from the planarizing device; and a mass spectrometercoupled to the transport means to receive the material and detect theatomic mass of the second substance.
 56. The apparatus of claim 55,further comprising a vaporizer having an inlet coupled to the transportmeans to receive the material, a heat source to vaporize the atoms ofthe first and second materials and form a vapor, and an outlet coupledto the mass spectrometer.
 57. The apparatus of claim 55, furthercomprising a fluid source in fluid communication with the platen toprovide fluid to the platen during planarization of the microelectronicsubstrate, wherein the transport means includes a conduit coupledbetween the platen and the mass spectrometer to move the fluid and thematerial removed from the microelectronic substrate to the massspectrometer.
 58. The apparatus of claim 55, further comprising acontroller operatively coupled to the planarizing device and the massspectrometer to control motion of the planarizing device upon receivinga control signal from the mass spectrometer.
 59. The apparatus of claim55 wherein the polishing medium includes a polishing pad having abrasiveparticles that are removed from the polishing pad during planarization,further comprising: a fluid source in fluid communication with theplaten to provide fluid to the platen; and a filter coupled to thetransport means between the platen and the mass spectrometer to removeat least a portion of the abrasive particles from the fluid.
 60. Anapparatus for detecting the endpoint of a planarizing process of amicroelectronic substrate having a first substance and a secondsubstance implanted in the first substance, comprising: a planarizingdevice having a first portion and a second portion movable relative tothe first portion to remove material from the microelectronic substrate,the material including atoms of the first and second substances; asource of impinging radiation located proximate to the planarizingdevice and having an aperture to direct the impinging radiation towardthe microelectronic device; and a detector spaced apart from themicroelectronic device to receive emitted radiation emitted by atoms ofthe microelectronic substrate while the atoms are attached to themicroelectronic substrate.
 61. The apparatus of claim 60 wherein one ofthe first and second portions of the planarizing device includes aplaten having a polishing pad adjacent thereto and the other of thefirst and second portions of the planarizing device includes a carrierthat releasably engages the microelectronic substrate with the polishingpad, the platen having a first aperture and the polishing pad having asecond aperture aligned with the first aperture to transmit theimpinging radiation to the microelectronic substrate and transmit theemitted radiation to the radiation detector.
 62. The apparatus of claim61, further comprising a solid transparent material in the aperture. 63.The apparatus of claim 62 wherein the solid transparent materialincludes a crystal.
 64. The apparatus of claim 60, further comprising acontroller operatively coupled to the planarizing device and thedetector to control motion of the planarizing device upon receiving acontrol signal from the detector.
 65. In a planarizing process of amicroelectronic substrate that includes a first substance, a method ofendpointing the planarizing process, comprising: incorporating an amountof a second substance into the microelectronic substrate by implantingthe second substance in the first substance and beneath a surface of themicroelectronic substrate; reducing a thickness of the microelectronicsubstrate by removing material from the microelectronic substrate toexpose the second substance; detecting the second substance by analyzingmaterial of the microelectronic substrate by detecting an intensity oflight at a selected wavelength emitted by atoms of the second substancepresent in a slurry, a vapor or in a matrix of the substrate bycomparing an intensity of light emitted by atoms of the second substanceto an intensity of light emitted by atoms of the first substance; andfurther reducing the thickness of the microelectronic substrate byremoving approximately the entire amount of the second substance fromthe microelectronic substrate.
 66. The method of claim 65 wherein atomsof the second substance have an electrical charge and implanting thesecond substance includes positioning the atoms of the second substanceproximate to a like electrical charge to accelerate the atoms of thesecond substance toward the microelectronic substrate.
 67. The method ofclaim 65 wherein implanting the second substance includes forming alayer of the second substance within the microelectronic substrate. 68.The method of claim 67 wherein forming a layer includes forming a layerhaving a thickness in the range of approximately 100 Angstroms toapproximately 500 Angstroms.
 69. The method of claim 67 wherein forminga layer includes forming a layer centered at approximately 200 Angstromsbeneath the surface of the microelectronic substrate.
 70. The method ofclaim 67 wherein forming a layer includes forming a layer having anumber of atoms of the second substance in the range of approximately0.1% to approximately 0.001% of the number of atoms of the firstsubstance.
 71. The method of claim 65 wherein detecting the secondsubstance includes detecting an intensity of light emitted by atoms ofthe second substance while the second substance remains implanted in themicroelectronic substrate.
 72. The method of claim 65 wherein detectingthe second substance includes detecting a layer of the second substance.73. The method of claim 65 wherein the surface of the microelectronicsubstrate is a first surface, the microelectronic substrate having asecond surface opposite the first surface, further wherein the firstsurface includes a first portion having a first height relative to thesecond surface and a second portion having a second height relative tothe second surface different than the first height, further wherein theact of implanting the second substance includes implanting a firstamount of the second substance at a first selected depth beneath thesurface of the microelectronic substrate at the first portion andimplanting a second amount of the second substance at a second selecteddepth beneath the surface of the microelectronic device at the secondportion, the first and second depths being approximately equal.
 74. Themethod of claim 73, further comprising ceasing to remove material fromthe microelectronic substrate after detecting the first and secondportions of the second substance.
 75. The method of claim 65, furthercomprising ceasing to remove material from the microelectronic substrateafter detecting the second substance.
 76. The method of claim 65 whereinthe first substance includes at least one of tetraethylorthosilicate andborophosphate silicon glass, further comprising selecting the secondsubstance from tungsten, aluminum and copper.
 77. In a planarizingprocess of a microelectronic substrate that includes a first substanceof tetraethylorthosilicate and borophosphate silicon glass a method ofendpointing the planarizing process, comprising: incorporating an amountof a second substance selected from the group consisting of tungsten,aluminum and copper into the microelectronic substrate by implanting thesecond substance into the first substance and beneath a surface of themicroelectronic substrate; reducing a thickness of the microelectronicsubstrate by removing material from the microelectronic substrate toexpose the second substance; detecting the second substance by analyzingmaterial of the microelectronic substrate by detecting an intensity oflight at a selected wavelength emitted by atoms of the second substancepresent in a slurry, a vapor or in a matrix of the; and further reducingthe thickness of the microelectronic substrate by removing approximatelythe entire amount of the second substance from the microelectronicsubstrate.
 78. The method of claim 77 wherein atoms of the secondsubstance have an electrical charge and implanting the second substanceincludes positioning the atoms of the second substance proximate to alike electrical charge to accelerate the atoms of the second substancetoward the microelectronic substrate.
 79. The method of claim 77 whereinimplanting the second substance includes forming a layer of the secondsubstance within the microelectronic substrate.
 80. The method of claim79 wherein forming a layer includes forming a layer having a thicknessin the range of approximately 100 Angstroms to approximately 500Angstroms.
 81. The method of claim 79 wherein forming a layer includesforming a layer centered at approximately 200 Angstroms beneath thesurface of the microelectronic substrate.
 82. The method of claim 79wherein forming a layer includes forming a layer having a number ofatoms of the second substance in the range of approximately 0.1% toapproximately 0.001% of the number of atoms of the first substance. 83.The method of claim 77 wherein the detecting includes comparing anintensity of light emitted by atoms of the second substance to anintensity of light emitted by atoms of the first substance.
 84. Themethod of claim 77 wherein detecting the second substance includesdetecting a layer of the second substance.
 85. The method of claim 77wherein the surface of the microelectronic substrate is a first surface,the microelectronic substrate having a second surface opposite the firstsurface, further wherein the first surface includes a first portionhaving a first height relative to the second surface and a secondportion having a second height relative to the second surface differentthan the first height, further wherein the act of implanting the secondsubstance includes implanting a first amount of the second substance ata first selected depth beneath the surface of the microelectronicsubstrate at the first portion and implanting a second amount of thesecond substance at a second selected depth beneath the surface of themicroelectronic device at the second portion, the first and seconddepths being approximately equal.
 86. The method of claim 85, furthercomprising ceasing to remove material from the microelectronic substrateafter detecting the first and second portions of the second substance.87. The method of claim 77, further comprising ceasing to removematerial from the microelectronic substrate after detecting the secondsubstance.